DX-52-1 according to Formula (I-1) shown below and derivatives thereof are known to have antitumor activity as described in U.S. Pat. No. 4,650,869. ##STR2##
However, DX-52-1 and derivatives thereof (hereinafter, collectively referred to as "DX-52-1 derivatives") decompose easily in an aqueous solution. For example, while DX-52-1 is relatively stable in an aqueous solution under an alkaline condition of pH 7 or above, long-term preservability and stability of DX-52-1 is not sufficient. It is therefore necessary to develop a long-term preservable and stable preparation of DX-52-1.